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Mini Bike Speed Calculator (MPH and KPH)

Required Data Entry
Drive Wheel Diameter MM  Inches 
Rated Engine RPM
Teeth On Axle
Teeth On Clutch

Calculated Results
Drive Wheel Circumference In Inches
Drive Wheel Circumference In MM
Gear Ratio
Maximum Speed In MPH
Maximum Speed In KPH
Version 1.4.9

This converter requires the use of Javascript enabled and capable browsers. The purpose of this calculator is to determine the potential speed of a mini bike based on certain data. Enter the diameter of the drive (power) wheel and tire combination. (Make sure the tire is properly inflated and in good condition.) The diameter is the radius * 2, or in this case, twice the distance from the ground to the center of the axle. Enter the published maximum rated sustainable RPM for the engine you are using. Standard "lawnmower" engines might be as few as 2400 and high performance engines as high as 9000 RPM. The majority are from 3000 to 4000 RPM. Enter the number of teeth or sprocket splines on the axle (higher number, probably 65 to 90) and on the clutch or engine (smaller number, probably 8 to 15). The ratio of those numbers yields the best power (faster acceleration) or the best high end speed, or a compromise of both. The higher the gear ratio, the higher the top end speed; the lower the ratio, the stronger the acceleration (power). Click on Calculate. The results are the circumference of the drive wheel/tire combo (in inches), gear ratio and the potential maximum speed (in MPH). Our default is for a "peppy", potentially street legal mini bike. The gear ratio is 6 and the potential speed is just under 36 miles per hour.

Applicable Calculator Formulae

PI = 3.14159
PI * D = C (3.14159 * wheel/tire diameter = circumference of wheel and tire combo)
at / ct = GR (gear ratio = axle teeth / clutch or engine teeth)
RPM / GR = WRPM (engine RPM / gear ration = Wheel RPM)
C / 12 = Cf (circumference of wheel/tire combo in feet = circumference / 12 inches)
FPM = Cf * WRPM (wheel RPM * circumference in feet = feet per minute)
FPM * 60 = FPH (feet per minute * 60 minutes = feet per hour)
FPH / 5280 = MPH (feet per hour / 5280 feet = miles per hour)

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